1. Field of the Invention
The present invention relates to a vibratory angular rate sensor.
2. Description of the Related Art
Vibratory angular rate sensors (gyrosensors) are recently in much demand for application to vehicle control and navigation because of their lower cost and smaller mass in comparison with other types of angular rate sensor. As described in Japanese Patent Publication 2002-139322 and U.S. Pat. No. 5,806,364, the vibratory angular rate sensor utilizes the Coriolis effect on a vibrating element that oscillates along a first direction by measuring its oscillation along a second direction perpendicular to the first direction. In the known vibratory angular rate sensor, the angular rate is detected in the form of a modulation of a sinusoidal waveform of reference frequency with the amplitude of the oscillation along the second direction. However, frequency components other than the fundamental frequency are generated in vehicular environment due to a number of factors. To remove the undesired frequency components, the synchronous detection technique is used to extract the fundamental frequency component from the amplitude-modulated signal using clock pulses synchronized to the fundamental frequency. However, the current vibratory angular rate sensor is still not satisfactory for vehicular application because the zero-point level of the detected angular rate fluctuates. Further, the detected angular rate suffers from phase instability.
Therefore, a need does exist to provide a vibratory angular rate sensor capable of detecting angular rate without zero-point fluctuation and phase instability.